Summary of Marketable Securities by Asset Type (Detail) - USD ($) $ in Thousands	Aug. 31, 2016	May 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	$ 155,477	$ 151,616
Available-for-Sale Securities, Gross Unrealized Gains	5,216	5,522
Available-for-Sale Securities, Gross Unrealized Losses	(7,208)	(10,182)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	153,485	146,956
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	132,878	129,025
Available-for-Sale Securities, Gross Unrealized Gains	4,776	5,171
Available-for-Sale Securities, Gross Unrealized Losses	(7,111)	(10,102)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	130,543	124,094
Equity securities \| Stocks \| Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	4,989	5,051
Available-for-Sale Securities, Gross Unrealized Gains	180	439
Available-for-Sale Securities, Gross Unrealized Losses	(53)	(247)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	5,116	5,243
Equity securities \| Stocks \| Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	30,896	27,717
Available-for-Sale Securities, Gross Unrealized Gains	2,613	3,831
Available-for-Sale Securities, Gross Unrealized Losses	(866)	(911)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	32,643	30,637
Equity securities \| Mutual funds \| Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	35,923	35,903
Available-for-Sale Securities, Gross Unrealized Gains	932	802
Available-for-Sale Securities, Gross Unrealized Losses	(2,828)	(4,357)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	34,027	32,348
Equity securities \| Mutual funds \| Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	61,070	60,354
Available-for-Sale Securities, Gross Unrealized Gains	1,051	99
Available-for-Sale Securities, Gross Unrealized Losses	(3,364)	(4,587)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	58,757	55,866
Fixed maturity
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	22,599	22,591
Available-for-Sale Securities, Gross Unrealized Gains	440	351
Available-for-Sale Securities, Gross Unrealized Losses	(97)	(80)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	22,942	22,862
Fixed maturity \| U.S. Treasury and other government
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	21,770	21,704
Available-for-Sale Securities, Gross Unrealized Gains	289	214
Available-for-Sale Securities, Gross Unrealized Losses	(97)	(80)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	21,962	21,838
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	829	887
Available-for-Sale Securities, Gross Unrealized Gains	151	137
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	$ 980	$ 1,024

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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